First of all,
Are you going to let them free range in your yard?
If not, do you have a very large space for them to run around in?
How are you going to manage all of the poop?
Yes... ducks LOOVVEE to swim! I can't think of anything they like more, for young ducks, you can start off with a kiddie pool, or for ducklings, I used a paint roller container, it's got a deep end and a shallow end for them to get out. How old are these ducks and what breed? Ohh Ohh... and what gender?
I still have a kiddie pool for my 5 ducks (2 muscovies, 1 Pekin, 2 Khaki Cambells) and they love swimming in that, but they also have a spa I bought for $25 off
eBay that they love! They love diving, so if you could get something that is quite deep they'll thank you for it.
I'm really glad you decided to take on duck... they are so amazing!
There is a site on the forum on treats for ducks, if I find it I'll post the link.